The present invention relates to a viewing angle compensator for a liquid crystal display capable of diminishing the viewing angle dependency of the liquid crystal display.
Liquid crystal display is occupying an important position in the display field, taking the place of the cathode-ray tube, because of such characteristic features as being driven at a low voltage, light weight and low cost. However, since the liquid crystal display adopts a method of displaying images by utilizing orientating behaviors of a liquid crystalline substance having an optical anisotropy, it inevitably involves the problem (hereinafter referred to as "viewing angle dependency") that the color tone of screen changes according to directions of seeing the panel. The viewing angle dependency becomes more conspicuous when a color compensating optical element such as a stretched film or a liquid crystal cell is mounted to the liquid crystal cell. For example, in the case of a lap-top type personal computer or a word processor display, utilizing a twisted nematic mode ("TN" hereinafter) or a super-twisted nematic mode ("STN" hereinafter), relatively good images are obtained when the screen is seen from the front, but when the screen is seen from a direction other than the front, the screen is colored or it becomes difficult to see images on the screen. Such viewing angle dependency of the display is not only undesirable to users but also is an obstacle to the realization of a larger screen which is required for a wall-mounted TV or the like. In the case of a large screen display, as long as the prior art is used, it is impossible to obtain clear images throughout the entire screen because the marginal portion comes to have a certain viewing angle even when the screen is seen from the front.
As means for diminishing such viewing angle dependency of the display, it has been suggested that the use of a film having a refractive index in the thickness direction larger than an intra-plane refractive index. [M. Akatuka et al.: Japan Display '89, 336 (1989)]. Actually, however, such a film is scarcely existent, and even when it is existent, the difference between the refractive index in the thickness direction and an intra-plane refractive index is 0.001 or so at most (Japanese Patent Laid Open No. 85519/1991), and thus an outstanding effect of remedying the viewing angle dependency has not been obtained yet. As a substance having a large refractive index anisotropy, a liquid crystalline substance is promising, but it has been considered that in the case of a low molecular liquid crystal, it is difficult to maintain a stable orientation, while in the case of a high molecular liquid crystal, it is impossible to obtain a uniform orientation.
Taking note of a liquid crystalline film having a large refractive index in the thickness direction in order to diminish the viewing angle dependency of a liquid crystal display, the present inventors have made extensive studies for obtaining a new liquid crystalline polymer which satisfies the said condition. As a result, the present inventors found out that films of a group of liquid crystalline polymers, including a ferroelectric and antiferroelectric liquid crystals proposed previously by us could take a structure having a large refractive index in the thickness direction. In this way we accomplished the present invention.
It is the object of the present invention to provide a compensator for a liquid crystal display, particularly a viewing angle compensator for a liquid crystal display using a liquid crystalline polyester film with orientation solidified.